The present invention relates to a novel water-base agrochemical composition containing a unique polyether-modified silicone compound. More particularly, the invention relates to a water-base agrochemical composition containing a unique polyether-modified silicone compound as a spreader agent for the agricultural chemical compound as the effective ingredient in the composition and suitable for spraying over agricultural fields, of which the polyether-modified silicone or organopolysiloxane compound is capable of exhibiting high surface activity in an aqueous medium with good stability over a wide range of the pH value of the water-base agrochemical composition.
It is a very common practice that water-base agrochemical compositions in the form of an aqueous solution or emulsion applied to the plants in the agricultural fields and orchards are almost always formulated with a spreader or tacker in order to improve spreadability of the agrochemical composition with good uniformity over the plants so as to ensure high herbicidal, insecticidal and pesticidal effects.
The spreader agents conventionally formulated in a water-base agrochemical composition are each a surface active agent by which the water-base composition is imparted with a decreased surface tension so as to promote uniform adherence of the agricultural chemical to the body of the plants within a short time. Various types of surface active agents are heretofore proposed and employed as an agrochemical spreader including polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers and polyoxyethylene higher fatty acid esters.
Besides the above mentioned polyoxyethylene-based surface active agents, silicone-based surface active agents are highlighted in recent years as an agrochemical spreader agent for water-base agrochemical compositions in respect of their high surface activity and low toxicity against human body. For example, Japanese Patent Kokai 6-55642 proposes a silicone-based spreader agent for a water-base agrochemical composition which is an organotrisiloxane compound expressed by the general formula EQU (Me.sub.3 Si--O--).sub.2 SiMe--[--C.sub.3 H.sub.6 --O--(--C.sub.2 H.sub.4 --O--).sub.p --R],
in which Me is a methyl group, R is a hydrogen atom or a methyl group and the subscript p is a positive integer of 6 to 10.
The applicability of the above defined polyoxyethylene-modified organotrisiloxane compound as an agrochemical spreader agent, however, is very limited because an aqueous solution of the compound exhibits surface activity only when the aqueous solution has a pH at or in the vicinity of neutrality and the surface activity of the aqueous solution thereof is decreased or lost when the solution is acidic or alkaline as is reported in Pesticidal Science, volume 38 (1993), pages 103-122. When the aqueous solution of the silicone compound has a pH value lower than 5 or higher than 9, for example, the surface activity of the aqueous solution is lost within only 24 hours of standing at room temperature. Reportedly, the mechanism for this surface activity degradation is presumably that a siloxane-rearrangement disproportionation reaction takes place in the molecules of the trisiloxane compound resulting in the formation of hexamethyl disiloxane on one hand and a diorganopolysiloxane of a larger molecular weight on the other hand. Accordingly, it is usually important that the spreader-formulated water-base agrochemical composition is prepared by admixing the silicone compound, immediately before use of the composition in the fields, to a master composition or that the pH value of the spreader-formulated water-base composition is kept at or around neutrality by using a suitable buffer solution.
It is sometimes the case, however, that a spreader-formulated water-base agrochemical composition can not always be actually employed just after preparation by the admixture of the silicone compound, for example, due to a sudden change in the weather for raining necessitating postponing of actual application of the ready-prepared composition which must be replaced with a new preparation when the weather is recovered. The use of a buffer solution to ensure neutrality of the water-base composition is also not free from a serious disadvantage because the agricultural chemical compound as the effective ingredient of the water-base composition is necessarily limited to those compounds having stability at neutrality since even weak acidity or weak alkalinity of the water-base composition is detrimental against stability of the compound.